1,112 research outputs found
Anatomy of recent and peatified Calluna vulgaris stems: implications for coal maceral formation
Quantified HI Morphology II : Lopsidedness and Interaction in WHISP Column Density Maps
Lopsidedness of the gaseous disk of spiral galaxies is a common phenomenon in
disk morphology, profile and kinematics. Simultaneously, the asymmetry of a
galaxy's stellar disk, in combination with other morphological parameters, has
seen extensive use as an indication of recent merger or interaction in galaxy
samples. Quantified morphology of stellar spiral disks is one avenue to
determine the merger rate over much of the age of the Universe. In this paper,
we measure the quantitative morphology parameters for the HI column density
maps from the Westerbork observations of neutral Hydrogen in Irregular and
SPiral galaxies (WHISP). These are Concentration, Asymmetry, Smoothness, Gini,
M20, and one addition of our own, the Gini parameter of the second order moment
(GM). Our aim is to determine if lopsided or interacting disks can be
identified with these parameters. Our sample of 141 HI maps have all previous
classifications on their lopsidedness and interaction. We find that the
Asymmetry, M20, and our new GM parameter correlate only weakly with the
previous morphological lopsidedness quantification. These three parameters may
be used to compute a probability that an HI disk is morphologically lopsided
but not unequivocally to determine it. However, we do find that that the
question whether or not an HI disk is interacting can be settled well using
morphological parameters. Parameter cuts from the literature do not translate
from ultraviolet to HI directly but new selection criteria using combinations
of Asymmetry and M20 or Concentration and M20, work very well. We suggest that
future all-sky HI surveys may use these parameters of the column density maps
to determine the merger fraction and hence rate in the local Universe with a
high degree of accuracy.Comment: 12 pages, 5 figures, 1 table, accepted by MNRAS, appendix not
include
Measuring the cosmic ray acceleration efficiency of a supernova remnant
Cosmic rays are the most energetic particles arriving at earth. Although most
of them are thought to be accelerated by supernova remnants, the details of the
acceleration process and its efficiency are not well determined. Here we show
that the pressure induced by cosmic rays exceeds the thermal pressure behind
the northeast shock of the supernova remnant RCW 86, where the X-ray emission
is dominated by synchrotron radiation from ultra-relativistic electrons. We
determined the cosmic-ray content from the thermal Doppler broadening measured
with optical spectroscopy, combined with a proper-motion study in X- rays. The
measured post-shock proton temperature in combination with the shock velocity
does not agree with standard shock heating, implying that >50% of the
post-shock pressure is produced by cosmic rays.Comment: Published in Science express, 10 pages, 5 figures and 2 table
A New Approach to the Optimal Target Selection Problem
Optimally selecting a subset of targets from a larger catalog is a common
problem in astronomy and cosmology. A specific example is the selection of
targets from an imaging survey for multi-object spectrographic follow-up. We
present a new heuristic algorithm, HYBRID, for this purpose and undertake
detailed studies of its performance. HYBRID combines elements of the simulated
annealing, MCMC and particle-swarm methods and is particularly successful in
cases where the survey landscape has multiple curvature or clustering scales.
HYBRID consistently outperforms the other methods, especially in
high-dimensionality spaces with many extrema. This means many fewer simulations
must be run to reach a given performance confidence level and implies very
significant advantages in solving complex or computationally expensive
optimisation problems.Comment: 10 pages, 14 figures, Extended version accepted to Astron. Astrophy
Models and implications for industry compensation in the restructuring of public transport in South Africa
Paper presented at the 33rd Annual Southern African Transport Conference 7-10 July 2014 "Leading Transport into the Future", CSIR International Convention Centre, Pretoria, South Africa.The concept of compensating existing public transport operators for the detrimental impact
of the roll-out of large-scale, publicly funded IPTNs on their businesses is valid. However,
the general approach to compensation adopted by South Africa to date is not financially
viable and has serious implications for future developments. Different compensation
models that look to align operators’ success, financial and otherwise, with that of the new
system they are incorporated into, must be considered and adopted going forward to
ensure the sustainability of the country’s public transport transformation programme.This paper was transferred from the original CD ROM created for this conference. The material was published using Adobe Acrobat 10.1.0 Technology. The original CD ROM was produced by CE Projects cc. Postal Address: PO Box 560 Irene 0062 South Africa. Tel.: +27 12 667 2074 Fax: +27 12 667 2766 E-mail: [email protected]
Towards a provincial public transport institutional framework for public and non-motorised transport transformation and improvement in the Western Cape
The Western Cape Government is currently developing a Provincial Public Transport Institutional Framework (PPTIF) to guide public and non-motorised transport improvement in the non-Metro areas of the Province. The framework aims to address the critical barriers to improving the current unacceptable state of affairs. The framework incorporates innovative approaches to tackling the challenges faced by the sector. Once the framework has been completed, it will be implemented.
The PPTIF differs from the Provincial Land Transport Framework (PLTF). The primary reason for the PLTF is to serve as a strategic management tool for the provincial transport department and includes the vision, objectives and policies of the department; current public transport strategies and sector strategies as well as associated financial, monitoring and institutional arrangements.
The PPTIF develops aspects of the PLTF in more detail, developing an institutional framework for achieving the improvement to public and non-motorised transport envisioned by the Department. The PPTIF also introduces innovative mechanisms for reducing cost and enhancing capacity to implement, which will inform future versions of the Provincial Land Transport Framework (PLTF).Paper presented at the 34th Annual Southern African Transport Conference 6-9 July 2015 "Working Together to Deliver - Sakha Sonke", CSIR International Convention Centre, Pretoria, South Africa.The Minister of Transport, South AfricaTransportation Research Board of the US
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